The present invention generally relates to superconducting structures, and more specifically, to low loss architectures for superconducting qubit circuits.
Superconducting quantum computing is an implementation of a quantum computer in superconducting electronic circuits. Quantum computation studies the application of quantum phenomena for information processing and communication. The basic building block of such a quantum computer is the quantum bit or qubit. As a generalization, a qubit is similar to the classical bit in that it is a system of two discrete states, which can be in the discrete quantum states |1> and |2>, as well as arbitrary superposition states. These discrete quantum states can be any set of two quantum mechanical levels, such as an electron spin or nuclear spin, or a pair of energy levels in an atom, ion or molecule. Similar to universal logic operations, there also exists a set of quantum gates which are universal, such that combinations of gates can realize complex quantum algorithms. A quantum gate is a generalization of a logic gate. However, the quantum gate describes the transformation that one or more qubits will experience after the gate is applied on them, given their initial state.
The electromagnetic energy associated with the qubit can be stored in so-called Josephson junctions and in the capacitive and inductive elements that are used to form the qubit. In one example, to read out the qubit state, a microwave signal is applied to the microwave readout cavity that couples to the qubit at the cavity frequency. The transmitted (or reflected) microwave signal goes through multiple thermal isolation stages and low-noise amplifiers that are required to block or reduce the noise and improve the signal-to-noise ratio. The microwave signal is measured at room temperature. The amplitude and/or phase of the returned/output microwave signal carry information about the qubit state, such as whether the qubit is at a ground state, an excited state, or a superposition of the two states.